The invention relates to a hermetically sealed housing for evaporation cooling of a power electronics.
Under the term xe2x80x9cpower electronicsxe2x80x9d an assembly unit of at least one electronic component is to be understood in this context, in which high electrical power is converted with the result that a large amount of dissipated energy or heat loss turns up. This heat loss has to be taken away reliably so that there will not occur an overheating of the power electronics. According to a preferred application of the housing according to the invention, the power electronics concerns the DC inverter of a so-called starter generator for a combustion engine of a motor vehicle, which combines the components starter and generator hitherto configured as separate parts.
When the evaporation cooling is used for cooling, the components of the power electronics are directly surrounded by a cooling liquid which is received in the housing where also the power electronics is arranged. The components to be cooled are preferably designed so as to have no housing, so that the cooling liquid has direct contact with those regions of the component where the heat loss turns up. In the case of semiconductor chips, it is the surface area of the silicon chip that is in direct contact with the cooling liquid.
The cooling liquid is selected such that it evaporates or boils during operation of the power electronics at those regions of the components where the heat loss turns up. The vapor bubbles produced rise and are condensed on cooler sections of the housing, so that they are again available for a renewed evaporation process. Such cooling method is particularly effective, because at the phase transition point of the cooling liquid from liquid to gaseous a very much larger amount of energy is absorbed as would be the case with solely a liquid cooling.
The problem with the evaporation cooling is that with each starting of the power electronics the temperature of the cooling liquid rises and, as a consequence thereof, the inner pressure in the housing. This cyclic pressure load constitutes a considerable mechanical stress acting on the housing. When such a housing is provided for being used in motor vehicles, it must be guaranteed that the housing is still hermetically sealed even after an operating period of 15 years, because otherwise a cooling of the power electronics would not be guaranteed. The housing must also be diffusion-tight, because otherwise the cooling liquid could escape from the housing despite an intact mechanical sealing.
The object of the invention is to provide a housing for a evaporation cooling of a power electronics, which is hermetically sealed for a long period and nevertheless can be produced at favorable costs with simultaneously having a low weight.
To this end, there is provided a hermetically sealed housing for power electronics. The housing comprises a tank consisting of sheet metal, and a cover consisting of an aluminum material. The tank has a surrounding edge which is provided with a plurality of bending lugs, and the cover has a shoulder. The bending lugs engage at the shoulder whereby the cover is pressed against the edge of the tank so as to hermetically seal the housing. Using two different materials for the cover and the tank offers a series of advantages. Using two different materials for the cover and the tank offers a series of advantages. The tank can be manufactured from steel with low costs and with high strength and high diffusion tightness with respect to the cooling liquid, for instance as a deep-drawn sheet metal part. The latter can be provided at low expenditure with beads in the side walls and at the bottom, so that a high strength with respect to loads is obtained which result from a high internal overpressure in the housing. By using aluminum or an aluminum alloy for the cover, the latter is able to be produced with a high thermal conductivity at reasonable costs. The two parts can be connected with each other at low expenditure, namely by bending or crimping the bending lugs; the bending lugs automatically have the deformability which is required for bending, since they are part of the tank made of steel. A series of advantages result from the use of bending lugs for fixing the cover to the tank. On the one hand, this type of fixing is fail-safe. When the bending lugs are bent upwards and fix the cover to the tank, then it is ensured automatically that the two parts are pressed against each other with the necessary force, so that a good sealing effect is obtained. Unlike with a welding method, for instance, a costly subsequent check is not required. A further advantage of this type of fixing is that the power electronics disposed in the interior of the housingxe2x80x94as well as the cooling liquidxe2x80x94are not subjected to any stresses upon assembling tank and cover, and no contamination is introduced into the housing. This is not the case with a welding method, in which both a high thermal stress and a soiling of the interior of the housing occurs due to burning products. Finally, the type of fixing used is very advantageous with regard to the production costs and the production time required.
For a seal between the tank and the cover there may be advantageously used an adhesive sealing compound which is applied onto the edge of the cover or the tank and is mainly forced out of the contact gap upon assembling cover and tank. The remaining, thin layer of adhesive effects, apart from the desired sealing, a mechanical connection between tank and cover, because it is very resistant to shearing. As an alternative to the adhesive sealing compound, an O-ring seal or another profiled seal could also be used for sealing, which seal is arranged in a groove on the edge of the cover.
On its inner side facing the interior of the housing, the cover is preferably provided with a plurality of condensation ribs, so that an as large an area as possible is obtained for the heat transfer from the cooling liquid and the vapor bubbles generated in it, respectively, to the cover of the housing.
Preferably, the cover is provided on its outer side with a cooling channel running in the shape of a serpentine, so that a ducted cooling of the outer side of the cover is possible.
Advantageous designs of the invention will be apparent from the subclaims.